High quality golf club sets are produced and marketed in what is termed "matched sets", each golf club being constructed such that the flexing characteristics of the club will provide the same degree of "feel" throughout the set. Although "feel" is somewhat subjective, it is generally well accepted that a golf club which provides proper "feel" will aid the golfer in achieving: (i) optimum club head velocity and club head position at the point of ball impact--providing better overall shots; and (ii) greater uniformity from shot to shot--both of which will contribute to lower total scores. U.S. Pat. No. 4,070,022, the disclosure of which is incorporated herein by reference, is directed to a method for accurately quantifying relative "feel", based on the frequency of vibration of a specific shaft. After the frequency determinations are made, shafts are selected from a plurality of selected shafts in which the frequencies fall on a predetermined gradient formed by a plot of shaft frequency and shaft length, in which shaft frequency increases as shaft length decreases. Subsequent mating of the shafts with weight-matched club heads produces a set of matched golf clubs.
U.S. Pat. No. 4,122,593, directed to a further advance, eliminates the need for classifying and storing large quantities of shafts in which the lengths and frequencies had been measured as set forth in the '022 patent. In the '593 patent, oversize blanks are utilized, one for each shaft length. The frequency of the blank is determined and a prescribed amount is removed to obtain the desired length. The amount of length removed and its location (i.e., whether from the tip or butt portion of the shaft) determines the frequency of the final shaft--enabling the manufacturer to directly produce a shaft with a desired frequency. Even with the ability to directly produce shafts with predetermined lengths and frequencies, the supply of shafts for a "matched set" required that the club manufacturer select (based on experience with other clubs) the frequency level, swing weight, and club weight which could form the basis of a "matched set" to be evaluated in a test program. Utilizing a series of charts and graphs which correlated head weights to frequency, an employee with long experience (as to the further effects of hosel length and tip insertion depths on frequency level) could then determine what shafts to utilize for the "matched set" to be supplied for the club manufacturer's evaluation.